Automatic control apparatus



Dec. 13, 1966 .1.1. EVA-Ns ETAL AUTOMATIC CONTROL APPARATUS 14 Sheets-Sheet 1 Filed NOV. 2l, 1962 Dec. 13, 1966 J. T. EVANS ETAL AUTOMATIC CONTROL APPARATUS 14 Sheets-Sheet 2 14 Sheets-Sheet 3 OUTPUTS Il Il gip-w m) FIGA AO`B=r FIGA J. T. EVANS ETAL AUTOMATIC CONTROL APPARATUS FIG.3A

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AUTOMATIC CONTROL APPARATUS Filed NOV. 21, 1962 14 Sheets-Sheet 5 I'2'48 BINARYCODED DECIMAL COUNT-UP DECADE 95 9e 97 98 I lr/ l lJ j 99 T Q ;TRANSFER 1 DT- TRANSFERII lOl RESET x :couNT 13o TRIGGER -zo l 2 4 8 TRIGGER -lo COUNT-UP FIG.6

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AUTOMATIC CONTROL APPARATUS Filed NOV'. 21, 1962 14 Sheets-Sheet 6 I-245 BINARY-CODED DECIMAL COUNT-UP DECADE F" Ir F3 RESET TRANSFER COUNT-UP COUNT 2 4 5 I '8 oon TRIGGER I 0 I O I O TRANSFER COUNT TRIGGER RESET Dec. 13, 1966 J. T. EVANS ETAL AUTOMATIC CONTROL APPARATUS 14 SheetsSheet 7 Filed Nv. 21, 1962 JOFZOu moZmDOmm EFE.. n m

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Dec. 13, 1966 J. T. EvANs ETAL 3,291,970

AUTOMATI C CONTROL APPARATUS Filed Nov. 21, 1962 14 SheetS-Sheet 11 D/A n/A X CONVERTER CONVERTER FEED MOTOR CONTROL Dec. 13, 1966 J. T. EVANS -ETAL AUTOMATIC CONTROL APPARATUS Filed NOV. 2l. 1952 14 Sheets-Sheet 12 E nu E M w... T M C N D E 0 .n O A P E T M w m E T P M W N C S R 0 C l M o F A T o o T T F T S T G T A L U o S N I M A A. E Y l S O U I O E L D D O w M m w A m M n p A M S Z T C R R m @Vm M m w .m C P A M s i .r A om a AWA A wwmwww P 3 T s. R o lem hm m C O O F ml. .mm E m EH A A A L C T3 C ST PU Sl Y l I m M N C nl I/ EWUEA E ld O R nnuvSASMN Uh 3 M MV Wn Il I/WA l, l C @CWA l W N O A O .A M mlbw l y ISIP FIG.I3A

FIGURE FIGURE 9v FIGURE FIGURE 8 FIGURE IO Dec. 13, 1966 J. T. EVANS ETAL 3,291,970

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United States Patent 3,291,970 AUTOMATIC CONTROL APPARATUS John T. Evans and Leroy U. C. Kelling, Waynesboro, Va., assignors to General Electric Company, a corporation of New York Filed Nov. 21, 1962, Ser. No. 239,285 7 Claims. (Cl. 23S-151.11)

This invention relates to electronic automatic control systems, and more particularly, to numerical control systems for controlling the position of the cutting element of a machine tool relative to a workpiece.

Machine tool control equipment may be considered to fall into the separate categories of Numerical Contouring Control systems and Numerical Positioning Control systems. Numerical Positioning Control primarily diifers from Numerical Contouring Control because positioning solely requires a command containing information as to the ultimate location of a workpiece relative to a cutting element, whereas contouring requires commands containing information as to the rate of speed and the instantaneous direction of motion of a workpiece relative to a cutting tool. An example of the former type of system is contained in the co-pending patent application of Leroy U. C. Kelling, Serial No. 136,420, led September 5, 1961, now Patent No. 3,226,649, and assigned to the General Electric Company, assignee of the present invention. An example of the latter type of system appears in the co-pending patent application of Leroy U. C. Kelling, Serial No. 136,049, filed September 5,

1961, now Patent No. 3,248,622, and also assigned to the General Electric Company.

The invention described hereinafter is embodied. in a Numerical Positioning Control system. A large number of the features of this invention, however, are also applicable to Numerical Contouring Control systems.

Avn object of the present invention is to provide improved numerical control systems. This -object is carried out in a specific illustrative embodiment by providing an improved Numerical Postiioning Control system.

Although a large number of systems have been developed for numerical control of positioning apparatus, the present invention belongs to that class of numerical control systems wherein the commanded position of the apparatus and the actual position of the apparatus are accurately represented by the phase of a commandpand position signal, respectively. In this class of system, the apparatus is positioned in accordance with the difference in phase.

In order to provide a system capable of positioning apparatus over an extended range, for example, 100 inches, with an accuracy in the order of .0001 of an inch, it has been found advantageous to use several feedback servo loops, each covering a different range of motion and, therefore, providing varying amounts of resolution. The embodiment hereinafter described uses a plurality of resolvers coupled to respond to motion in each axis of apparatus travel.

The resolvers are arranged to express different ranges of machine travel by being coupled to experience -a complete revolution in response to different amounts of apparatus travel. Thus, a coarse resolver is coupled to experience a complete revolution in response to a full range of travel, for example, 1010 inches; a medium, or intermediate, resolver is coupled to experience complete revolutions in response to successive portions ofthe full l generates a position signal representative of the apparaice tus position with respect to a reference point, which consist of three components of vary resolution. In order to cooperate with these components of the position signal, the command sign-al is developed in three corresponding components which comprise a coarse, medium, and fine portion. Obviously, the particular range encompassed by each portion of the command signal is identical to the range encompassed by the individual resolvers in the feedback servo loops.

Once signals are developed which represent both the present and the desired position of the apparatus, the control system must provide means for utilizing these signals to most effectively move the apparatus t-o the desired position. The control system described hereinafter operates by instruction a rapid traverse of the feed mechanism until a position close to the command position is attained. In close proximity to the commanded position, the feed rate is decreased with the objective of reaching zero when the exact position is achieved. Obviously, initial comparisons between the commanded position and the actual position, to determine the direction of travel, may employ relatively coarse signals. In the embodiment to tbe described hereinafter, the coarse signal components are rst compared in order to make an initial determination as to the direction in which the equipment must move. Subsequently, the medium signais, and finally, the fine signals are compared in order to achieve accurate positioning.

Another object of the present invention is to provide improved means for comparing phase-coded signals and selectively generating control signals in accordance with particular characteristics of the respective phase-coded signals.

Yet another object of the invention is to provide means for comparing phase-coded signals having varying degrees of resolution and selectively generating control signals having Characteristics determined by the results of the comparison.

In the patent application, Serial No. 136,049, cited above, a positioning control system is disclosed wherein coarse comparison of the command signal with the position signal is accomplished by the establishment of zones and the determination of which zone the actual position falls within. By recognizing the different zones the position signal falls in, this positioning control system is Aable to determine how the machine mechanism should be controlled. When in close proximity to the desired position, a ne phase discriminator generates signals which are proportional to the deviation between actual position and desired position.

In contradistinction to the described patent application, the embodiment described hereinafter utilizes a plurality of command phase counters to develop the components of the phase-coded command signals. The output of each of these command phase counters is compared with the output of the feedback resolver having the corresponding range. A coarse end zone is developed by means associated with the coarse command phase counter. If the position signal is outside of thi-s coarse end zone (in the embodiment an illustrative area within i0.6 of an inch of the commanded position is adopted as the coarse end zone) a determination is made of the direction of traverse required, and a xed amplitude signal is applied to drive the feed mechanism in that direction. When the position signal is within the coarse end zone, signal comparison i-s shifted to the intermediate range components of the command and position signals. A plurality of intermediate end zones are then developed by means associated with the medium command phase counter. While the position signal is within the wider intermediate end zones, but not within a preselected narrower intermediate vend particularity in the appended claims.

plied to the feed mechanism. Once the position signal is Within the preselected narrower intermediate end zone a phase discriminator is used to compare the fine range components of the command a-nd position signals and control the application of a feed signal to the feed mechanism that is proportional to the difference between said signals.

Another object of the present invention is to provide an improved numerical positioning system wherein a plurality of end zones are developed within which respective components of the command and position signals are compared.

Yet another object of the present invention is to develop an improved numerical positioning control system wherein the coarse and medium components of a command and a position signal are compared to determine their mutual presence within preselected end zones; and

v wherein the fine components of a command and a posi- .zone, a second smaller fixed .amplitude feed signal is aption -signal are compared in a phase discriminator when both signals are within a preselected end zone, in order to develop a feed mechanism control signal which is commensurate with the difference between said phases.

An embodiment of the invention is described hereinafter in conjunction with an apparatus positoning system that operates in response to input data. The system includes coarse, medium, and fine command phase counters responsive to the input data to generate three phase-coded command signals representing a commanded position in dimensional ranges having successively finer resolution. Feedback resolvers and associated circuitry are coupled to the apparatus to generate phase-coded position signals representing the actual position in dimensional ranges equivalent to those of the command signals. A number of zone generating ip-flops are uniquely triggered when preselected numbers are registered in the command phase counter group to define zones within successively close-r proximity to the commanded position. Cooperating ip- Hops responsive to the position signals yield a discrete indication when the actual position of the apparatus is within these zones. Finally, control circuitry furnishes the signals to drive the apparatus into position with speeds determined by the zone in which the actual position resides.

The novel -features of the invention are set forth with The invention itself, however, both as to its organization and method of operation, together with further advantages and features thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a general block schematic showing the basic components present in an illustrative numerical positioning cont-rol system embodying the features of the invention;

Y FIGURE 2 is a somewhat more detailed block schematic drawing illustrating the components and novel features of the invention as embodied in the control section for a single axis of machine motion;

FIGURE 3 shows the symbolic representation of a flipop of the nature used in the following illustrative embodiment of the invention;

FIGURE 3A is a truth table describing the operation of flip-tiops such as symbolized by FIGURE 3;

FIGURE 4A shows the symbolic representation of a logic NOR circuit of the nature used in the following illustrative embodiment of the invention;

FIGURE 4B shows the symbolic representation of a logic inverter circuit of the nature used in the following illustrative embodiment of the invention;

FIGURES 5 through 7 and 5A, 6A and 7A show the symbols and typical logic diagrams of binary-coded-decimal counters of the type used in the following illustrative embodiment of the invention;

FIGURES 8 through 12 when arranged as shown by the sheet layout in FIGURE 13A comprise an-interconnected logic circuitschematic of an illustrative embodiment of the invention;

FIGURE 13 is a circuit schematic showing a number of the control relays and switching means used in conjunction with the circuit of FIGURES 8 through 12;

FIGURE 14 illustrates a typical piece of punched tape of the nature contemplated for presenting numerical input data;

FIGURE l5 is a timing diagram for sequence control signals utilized in the following illustrative embodiment of the invention;

FIGURE 16 is a diagrammatic illustration of a decade switch which may be used to formulate zero offset data for insertion `into command phase counters of the nature illustrated hereinafter;

FIGURE 16A is a chart showing the logic outputs for various positions of the switch shown in FIGURE 16;

FIGURE 17 is a graph showing apparatus velocity as a function of position error in close proximity to the commanded position; and

FIGURES 18 and 19 are timing diagrams illustrating pertinent signals that are operative in the automatic and semi-automatic modes of operation, respectively.

GENERAL DESCRIPTION illustration, a drill press 10 is illustrated ori the right of the ligure. It should be understood that the teachings of the invention are applicable to any machine control wherein the position of an operating machine element with respect to a workpiece is of importance.

The function of the entire system, as illustrated in FIGURE l, is to control machine tool 10` automatically in response t-o numerical data as read from a numerical data input equipment 16 appearing on the left of the ligure. Machine tool 10 comprises a cutting element 14 adapted to move in the vertical plane or along a Z axis. It further comprise-s a worktable adapted to move in a horizontal plane along both the X and Y axes. An X axis feed mechanism 12 and a Y axis feed mechanism 13 are illustrated for accomplishing this motion. During processing, a workpiece 11 is secured to the worktable of the machine and the table is thereafter positioned in accordance with the numerical data input for proper action by the cutting element 14.

The control system illustrated is adapted to control motion in both the X and Y coordinates. It will be obvious to those skilled in the art that motion in the Z axis, in addition to other control functions, may be easily performed in accordance with the teachings hereinafter.

All actions of the machine 10 are under the control of numerical data input equipment 16. For purposes of illustration, a punched tape input has been selected. Of course, other appropriate means may be used for presenting numerical data and these Iare also contemplated. A block of information on the punched tape, in accordance with the system to be described, contains all of the information necessary for one polsitioning operation. The data is presented in words, each of which has a letter address as the initial character. The characters in each word are made up of a plurality of simultaneously read elements encoded in the well-known binary form. An example of a w-ord calling for a particular position on the X axis might be X1`23456, wherein each of the characters is represented in binary form. The letter address X designates that the following numerical characters represent a position on the X axis. Consequently, when this letter address is detected, the following numerical characters are routed to X axis control .section of the control system for generation of command signals. Before proceeding with a consideration of the processing of the command signals, it is worthwhile to consider the servo loops which are involved in the control of each axis of motion of the machine control element; The X Vting element 14 with respect to the workpiece 11.

axis and Y axis servo loops are structurally independent of each other in their action of driving the feed mechanisms. Since the equipment throughout the system for the X coordinate is precisely the same as for the Y coordinate, solely the X coordinate control section will be described. As shown in FIGURE 1, corresponding elements of the Y axis control section have been given the same numerical designation as those in the X axis control section. They are. distinguished by a prime symbol The X coordinate servo loop comprises an X axis position servo 24, including a D.C. amplifier driving a servo motorwhich by its output shaft 26 controls a feed motor control to -actuate the Xaxis feed mechanism 12. Simultaneously, position servo shaft 26 drives the X axis multiple range position feedback resolvers 22. The output leads 27 ofthe multiple range position feedback resolvers provide an electrical representation of the position of the machine in the X coordinate since both the feed mechanism 12 and the multi-range position feedback resolvers 22 4are driven in common by the position servo 24. Leads 27 are coupled into the X axis end zone phase comparators 23. The function of the end zone phase comparators is to compare the position signal applied over lead 27 with a command signal applied from the X axis command generators. By comparing the phases of the command signal and the feedback posi- Vout the control system. Thus, one of the outputs of timing generator 17 is applied over lead 28 to the multiple range position feedback resolvers 22 and another of the outputs is applied over leads 29 and 30 to the command `phase generators 18, 19, and 20. In common with other systems utilizing phase comparison between control and position signals, the basic reference pulse train represents a standard signal and the phase deviations between this standard signal and the command and position signals representthe distances of the commanded position and the actual position, respectively, from a predetermined reference point.

As shown, the command signal is developed in a plurality of command phase generators 18, 19, and 20. The utilization 'of thesel three, lcom'mand phase generators corresponds to the use of multiplte-range position feediback. In order to obtain the desired accuracy and resolution, a plurality of feedback resolvers having varying ranges are employed. In cooperation, therefore, with this servo loop arrangement, a plurality of command phase counters having similarranges and resolution are used.

When operating, the numerical data input equipment supplies the command phase -generators with a number indicative of the commanded position to be assumed. This number is supplied via a read-in counter 21. Upon subsequent application of the pulse train rfrom timing gen- "erator 17, each command phase counter produces an output signal having a phase representative of the particular component of the command signal in its own range. These -components of the command signal are compared in end zone phase comparators 23 with the appropriate components from the multiple range-position feedback 6 resolvers 22 and develop the control voltages for position servo 24.

As pointed out hereinbefore, it is essential that an adjustable zero reference point be available. Means are incorpo-rated, as shown by X axis zero offset 25, for presetting into the command phase generators a number representative of the position in the X axis which is to -be considered the zero reference point.

A further item should be considered before proceeding to an examination of the more detailed block schematic in FIGURE 2. In the present system, the numerical data input equipment is assumed to provide command data with a resolution of .0001 of an inch for positioning up to inches. This requires six decimal digits. As designed, the equipment has a coarse, medium, and fine command phase generator. The three most significant digits of a command signal are stored in the coarse command generator 18 and the three least significant digits are stored in the line command phase generator 20. From these stored digits, an intermediate number is developed which has a range correpsonding to the intermediate resolver range of the multiple range position feedback resolver group 22. Thus, the medium command phase generator 19 does not receive information from the numerical data input equipment 16 but rather, from the coarse and fine command phase generators 18 and 20.

A more complete understanding of the unique features of the invention may -be gleaned from a consideration ofthe more `detailed blocks schematic in FIGURE 2. In this ligure, the numerical data input equipment 16 has been replaced -by Numerical Data Input Equipment 53. The command phase generators, end zone phase comparators, and multiple range position feedback resolvers have been illustrated in terms of their component parts. It will be noted that only the X axis control section is illustrated in FIGURE 2. This is because the other coordinates of motion are controlled by substantially similar circuitry.

As shown in FIGURE 2, the Numerical Data Input Equipment 53 comprises, a tape reader 31; a number recognition means 32 for recognizing numerical characters; an address `recognition means 33 yfor recognizing letter characters; and a sequence control means 34 for controlling information read-in and circuit operation in response to the input data. Thus, when an address is recognized, sequence control 34 operates to select the section of the control system to be rendered operative. Whe-n an X address appears, this selection results in control over the X axis command phase counters via lead 54. When other addresses appear, control is asserted over appropriate sections, as illustrated by lead 55 connected to Other-Axis Positioning Systems 52.

Sequence con-trol 34 resets the command phase counters to prepare the selected control section for the receipt of new command data. A signal is then generated to transfer the zero reference data to the appropriate command phase counters. This will be described shortly. Thereafter, the individual control characters are used. to preset read-in counter 21. As each character is determined by number recognition 32 to lbe numeric, read-in counter 21 operates to produce a series of pulses equal to the number preset therein for distribution via row counter and distributor 35 to the appropriate portions of the command phase counters 36 and 38.

Consideration should be given to the command phase counters 36, 37, and. 38. Three separate command phase counters are used to generate components of the command signal representative of various ranges. Each command phase counter is a binary coded count-up circuit operative to assume one thousand discrete permutations of output conditions. Furthermore, each comand phase counter comprises three separate decades which are operative in binary-coded-decimal form to count from 1 to 10. Thus, the application of successive pulses from a reference pulse train generator 70 causes the command phase counters are restricted to particular operating ranges.

.- to register number-s of successively higher value .until a full count is registered and an output is produced. The

`counting cycle continues as long as input pulses are apperiod of time commensurate with the number originally stored in the command phase counter. This being so, the output from each command -phase counter is a phase coded signal discretely representing the number originally stored therein.

Inv operation, the most significant three digits of a command are stored in coarse command phase counter 36 and the least significant three digits are stored in ne command phase counter 38, Thus, the outputs from the command phase counters represent coarse and fine components of the original command data. A medium command phase counter 37 is selectively supplied from both the coarse and ne command phase counters to register an initial count of intermediate value and. in response to input pulses generates a phase coded signal in the intermediate range.

The diagram in FIGURE 2 includes numerical notations representative of specific dimensions or valves which have been adopted for purposes of describing circuit operation. The reference pulse train generator 70 has the parenthetical notation 250 kc. adjacent thereto. -This indicates that the pulse train therefrom is assumed to have a repetition rate of 250 kilocycles per second. Also, the

command phase counters are divided into three blocks each having parenthetical notations. In coarse command phase counter 36, for example, these are 0.1, 1, and 10. These notations indicate that the decades represented by each of these blocks register numbers wherein each bit or element of the respective decade is assigned the decimal weights of 0.1, l, and l0, respectively; the decimal values representing apparatus position in inches. Further, the resolvers 43, 44, and 45 are accompanied by the paren- Y thetical expressions: 100"/rev, 2"/rev, and 0.1"/rev, re-

spectively. These expressions indicate that a single revolution of any one of these resolvers represents the cited distance of travel.

An understanding of the typical operations within any one control section may be best illustrated by considering a cycle of operation.

Upon the application of power, reference pulse train generator 70 delivers a pulse train having a repetition rate of 250 kilocycles per second to both pulse rate divider 50 and the command phase counters. The effect of these pulses upon the feedback circuitry which generates the actual position signal will first be considered.

Pulse rate divider 50 is a divide-by-1000 device of a nature well known in the art. The output of this device, a pulse train having a repetition rate of 250 cycles per second, is applied to a resolver supply 51. The function of resolver supply 51 is -to develop an appropriate input signal for each of the resolvers 43, 44, and 45. These resolvers are conventionally energized by a pair of equal amplitude sine wave signals having a 90 phase difference therebetween. Effectively, this phase difference permits the application of a sine and cosine signal to the orthogonally disposed windings of the resolvers. As a result of resolver action, the specific position of the rotor causes the generation of an output in a secondary winding which has a phase with respect to the original signal from pulse rate divider 50 that is directly proportional to the amount of rotation of the rotor. Thus, each of resolvers 43, 44, and 45 generates an output signal having a phase displacement commensurate with the position of the machine element they are monitoring.

Due to the coupling between the X axis feed mechanism 12 and each of the resolvers, their output signals Resolverr Ano greater than 50:1.

45 is coupled to the X `axis feed mechanism by means schematically illustrated by line 56 to produce a complete revolution for 0.1 of an inch of apparatus travel.

Resolver 44 is coupled to the X axis feed mechanism by means schematically illustrated by line 57 and gearing v mechanism 47 to produce a complete revolution in re- `by gearing 46, and 47 which are shown to have a 50:1

ratio and a 20:1 ratio, respectively.

It should be noted that the ratio between resolvers is Ithas been found, after taking into consideration the multiplicity of factors which affect the resolution available from individual resolvers andthe circuitry associated therewith, that it is expedient to so limit the ratio. It has been found, for example, that a ratio of 100:1 may not be efficiently utilized in spite of the fact that the individual resolvers can easily provide resolution of the nature required to use this coupling ratio in a system having the above stipulated accuracy.

Returning to circuit operation, it is established that coarse resolver 43 is producing a 250 ,cycle per .second signal having a phase representative of the apparatus position within a 100 inch range; medium resolver 44 is producing a 250 cycle per second signal having a phase representative of the apparatus position within a 2 inch range; and fine resolver 45 is producing a 250 cycle per second signal having a phase representative of the position of the apparatus within a 0.1 of an inch range. These signals are individually applied to a coarse end zone com parator 40, intermediate end zone comparators 41, and phase discrminator 42,`respectively.

Upon recognition in address recognition circuitry 33 of a data word containing information for the X axis control mechanism, sequence control 34 applies signals to reset each of the command phase counters 36, 37, and 3S associated with the X axis control section. These counters are then preset with numbers representing the sum of zero offset to the desired reference point and the commanded position.

As previously mentioned, the workpiece may be attached to the table of the machine in different positions and consequently, a reference must be established in each direction of traverse.v Simple means have been developed wherein values may be applied to each decade of the I tozero,sequence control circuit 34 generates a signal to transfer the numbers stored in the zero offset switches directly into the command phase counters they are individually associated with.

The tape orother data presentation means is thereupon stepped to its next position and assuming that a number is recognized by number recognition circuit 32, the data representative of that number is preset into readin counter 21. Read-in counter 21 is a simple decade counter operating in the same binary-coded-decimal system in which the data is presented. `Under the control of sequence control' 34, once read-in counter 21 has received a complete character, pulses from' pulse rate divider 50 on lead 62 are applied at a relatively high repetition rate to start counting therein. In response to this counting, output pulses equal to the number preset are supplied from read-in counter 21 through row counter and distributor 35-to the appropriate decade of the cominand phase counter. If it is assumed that the first number read is the most significant digit of theV command, this is recognized and the output pulses are routed from .read-in. counter `21 to the (10) decade of coa-rse cornmand phase counter 36. It will be recalled that the command phasecounters are count-up circuits and consequently, the` application of the pulses from read-in counter 21 to yany one of the decades is effective to increase the, number originally stored therein -by the zero offset means bythe number read from the numerical vd'ata input equipment.

As successive-numerical characters are read from the input equipment, they are first set into read-in counter 'destaco 21 and thereafter countedout in response to pulses from is changed from nine to zero, this also results in a carry tothe next most significant decade. It should be recognized that in the system illustrated, only six decimal digits are' employed. Subdividing this into coarse and fine components yields three-,deci-mal'digits for the coarse component and three decimal digits for the fine component. y

In the system contemplated herein, these components are stored under the -control of the row counter and distributor .'35 directly into the coarse Vand line command i phase counters 36 and 38, respectively.v However, be-

cause the desired accuracy `and design efficiency have l led` to the design of a three-part feedback signal system, intermediate range figures "are needed. In order to develop lsuch intermediate range figures, binary'values are selectively extracted from both the coarse andine com- `mand phase counters and applied as inputs to medium command phase counter 37'.

i As shown, medium commandv phase counter 37 is preset -by a number of outputs lfrom the coarse and fine 'command phase counters 36,' 38 vi'a a plurality of leads schematically illustrated by lead 59 and lead y60. The read-in of this informationl to the medium command phase counter is effected after the other counters are preset and before the command signal is generated.

When each of the command phase counters stores a number representative of the sum of the commanded position plus the zero offset, sequence control 54 generates appropriate signals for the transfer of selected portions of each digit in the coarse and line command phase counters into medium command phase counter 37'. Upon completion of this operation, thev command phase counters register numbers inl binary-coded-decimal form Arepvvresentative of the commanded position in a coarse, me-

dium, and fine range. i p

Sequence control 34 supplies an actuating signal which kgates the pulse train 'from generator 17-into each of the command phase counters 'and they begin to count up. Command ph-ase counters are recognized `in the-art and theiroperation maybe easily understood. Since -each command phase counter comprises't'hree binary-codeddecimal decades,they divide the input'by one thousand and an output pulse may be extracted from the vlast decade which has a frequency equal to /go@ of the input frequency. This output appears at an instant of time such that the time between this appearance and the occurrence of the one thousandth pulse applied to the command phase counter is proportional to the originally registered nu-mber. If the output is compared with a signal derived by simply dividing the input signal by one thousand, there is a phase difference commensurate in magnitude .With lthe magnitude of the originally registered number. The

apparatus comes within 4a preselected end zone.

' X axis positioning motor 49. l

difference ybetween the signal from a command phase counter and a `reference position is indicated by the amount by which the command signal leads the reference signal. Thus, comparison of the output from each of the command phase counters with the output from the resolvers is effective to provide an error signal which represents the difference between the commanded position and the actual position. Once the error signal is available, means are req'uiredto convert it toa form for use in driving the feed mechanism.

p In numerical positioning control, it is customary to drive fthe positioningffeed Imechanism at a constant rate of speed over the` major portion of any distance to be traversed. For this reason, the generation 'of analog voltages proportional to the error between two widely divergent positions `is. generally unnecessary. The present invention,recognizing this fact, establishes end zones vWithin which specialfconsideration is given to the phase diilerence between the command and position signals, and outside of which, only the basic determination of whichsignal is leading is made. For large differences y'between the command and position signals, a single output is provided which drives the feed mechanism in either required direction at a constant rate of speed until the Once within this zone, comparison ismade between the sig- 'nals of the 'intermediate command phase counter and feedback resolver to accurately determine the direction of traverse and thereafter, when within a more sharply defined end zone, the fine resolution command signal and `feedback signal are used to develop an analog signal having a magnitude proportional to the amount of error.

Thus, the machine feed mechanism and? control system `are designed tocooperate completely -without developing more information than is necessary, and with the necessary information being developed as economically and eiciently as possible. 4 It should be understood that in some instances it is advantageous to develop analog signals to drive the feed ymechanism over-a larger errorl range than that illustrated herein. Iny this case, phase dscriminators may be ern- 'ployed to develop analog error'signals in response to -comparison of the medium, or even the coarse, command vand position signals.

As shown in FIGURE-2 of'zthe il1ust`rati\'e embodi- "rnent, coarse end zone comparison and intermediate end Zone comparison is handled in blocks 40 and 41. There- -H after, a phase discriminator 42 compares the fine cornponentof the command signal and the tine component of the feedback signal-and supplies an analog Voltage to a pulse-time-to-current converter 48l which in turn drives the l With the general functioning of the proposed `numerical positioning control system in mind, a more complete understanding will'be availablel from a consideration of a specific circuit designed to perform the described functions. Of course,`equivalent elements may be sub- "stituted by those'skillcd in the art for the particular 'elements employed. The specificy circuitry illustrated in the circuit schematic composed of FIGURES 8 through 13, and described hereinafter, is merely by way of example. v f

` DETAILED DESCRIPTION l Circuit symbology Several techniques havebeen used to make it easier to follow the operation -of the illustrative circuit. 'For convenience in locating the elements of the circuitry and as an aid in recognizing the function of these elements, they have been given a two-part designation. In this designation, the numerical prefix represents the figure in which the element appears and the alphabetical suiiix is generally descriptive of the function performed by the particular circuit element. For example, element 9-EOB is a iiip-op in FIGURE 9 which is set at the ments in each figure.

, line symbol.

End Q f eachlock of data The lead designationswand "other elements also bear numerical prefixes indicative of the figure in which they originate; however, numerical sufiixes are used to differentiate between the various ele- As a further aid in recognizing the [leads over which I example, lead 9 10 in the lower central portion of FIG` y URE 9, is designated mmand Reset.

This indicates that the signal for resetting the command phase counters is transmitted via this lead. Also, when a bar is placed v above this type of functional lead description, it indicates f that the operative signal is a logic 0. The absence of such a bar indicates that the operative signal is. a logic l. In connection With the control relays, shown primarily in FIGURE 13, it will be seen that the detached contact formof illustration has been used. This type of illustration lends itself to increased clarity of circuit description and a `more complete understanding of circuit operation by physically locating the contacts of a relay in the areas of a circuitwhere their operation performs an operative function. The contacts bear the same desig- It is well known that any Boolean equation can be synthesized with NOR logic exclusively. A gate for performing this logic operation is shown by the symbol in FIG- URE 4A having inputs A and B and output C. Simply, this logic function can be defined as follows: If the A input or the B input, or both, have a logic value 1 applied thereto, then the output C has the logic value of 0. Stating it another way, the output C is equal to logic l if 4neither the input A n o r the input B has the logic value 1.

vFIGURE 4B is a single input NOR circuit. This is an inverter, but the not-ation utilized is the same as that for FIGURE 4A. The output B of the inverter always takes `the opposite logic value from that of t-he input A.

-There are many different circuits for developing the logic components represented in FIGURES 4A and 4B. However, particularly useful transistor NOR circuits for Vuse in this numerical positioning control system are disclosed in a standard text on transistorized digital logic components entitled, Design of Transistorized Circuits for Digital Computers, byl Abraham I. Pressman, John F. Rider, Publisher, Inc., New York, 1959.l More particularly, a preferred two input transistor NOR circuit is nation as the relay winding and are therefore easily identiied. In the drawings, normally open contacts `are` illustrated by a pair of short parallel lines orthogonally inserted in the series `path they interrupt when operated,

and normally closed contactsy are similarly illustrated'- with an additional slanting line intersecting the parallel In FIGURE 13, contacts 13-ZO0 in the energizing circuit of ready-to-read relay 13-RTR represent typical normally open contacts and contacts 13- `ATO and 13-MAN in the energizing circuit of the semiautomatic mode relay 13,-SEM represent normally closed shown in FIGURES-1, at page 8'l9l. The inverter of FIGURE 4B may be developed by having solely one input to the NOR circuit of FIGURE 8-l of the Pressman test. It is often the case that the NOR package must handie more than two input variables. This is very easily accomplished since two or more NOR circuits may beiplaced in parallel to provide the required function,

each of the NOR circuits has a transistor amplifier therein,

whereby appropriate potential and current values are applied. The logic value 1, on the other hand, is represented by azero or negative voltage. i This notation is consistent with the practice followed in the authoritative text on logic switching and design by Keister, Richie, and

Washburn, entitled, The Design of Switching Circuits, D. Van Nostrand and Company, 1951.

The timing diagrams in FIGURES 15, 18, and 19 are illustrated in accordance with the described convention. Thus, the basic level, whichcorresponds to a zero voltage, represents a logic 1; the raised or pedestal level, which specific circuit configurations may be developed by those skilled in the art-tol perform the functions designated by the various circuit symbols. The voltages supplied to operate the circuits are, of course, dependent upon the illustrated in FIGURES 3 through 7. Any number of L A typical bistable multivibrator or flip-flop, used primarily for storage or memory, is shown in FIGURE 3. This Hip-flop may be developed in accordance with the circuit in the Pressman text shown in FIGURE 11-7, vat page ll-296, by opening each of the two loops connecting each of the output leads with its input steering lead.

v:Set and Reset inputs may be implemented by applying two input signals to the bases of the two transistorsof the flip-flop, respectively, through a series resistor connected to each base terminal. The logic of the multivibrator of FIGURE 3 is completely represented in the truth table of FIGURE 3A. n

The truth table is divided into three horizontal sections. The first of these sections, designated on the left as Set- Reset, illustrates the logic output conditions for various logic inputs on the iiip-iiop Set (S) and Reset (R) terminals. The second horizontal section, designated Joint Triggering, illustrates the logic output conditions when specific components employed; consequently, only the `polarity ofthe voltage source is shown in the circuit logic 0 inputs are maintained on terminals S and R and triggering impulses (voltage transitions from a logic l to a logic 0) are simultaneously applied to the Set Trigger (ST) and Reset Trigger (RT) terminals, while various logic values are applied to the Set Steering (SS) and Reset Steering (RS) terminals. The third horizontal section, designated Separate Triggering, illustrates the logic symbols are used. For example, is less than )...1

'1 .Thesel symbols do not convey the degree of difference in magnitude, only the sense of the difference.

All 'digitalr logic circuits require' devicesto perform bistable multivibratorsor flip-flops represented in FIG- f URE 3.

output conditions when logic O inputs are maintained on terminals S and R and triggering impulses are independently applied to the ST and RT terminals;

The vertical columnsin the truth table of FIGURE 3A represent the logic conditions at the various terminals of a typical flip-flop, In general, this is self-explanatory; however, with respect to the columns designated Outf puts, it should be noted that the condition of the iiip-iiop outputs before'` and after the application of an operative input is indicated. Thus, the representation ln indicates the state of the output lead 1 prior tothe application 

1. IN AN OBJECT POSITIONING SYSTEM WHEREIN A COMMANDED POSITION OF SAID OBJECT IS REPRESENTED BY A PHASECODED COMMAND SIGNAL AND THE ACTUAL POSITION OF SAID OBJECT IS REPRESENTED BY THE PHASE-CODED POSITION SIGNAL, MEANS FOR ASCERTAINING THE PRESENCE OF SAID OBJECT WITHIN A PRESELECTED DISTANCE FROM SAID COMMANDED POSITION COMPRISING, A FIRST BISTABLE ELEMENT NORMALLY RESIDING IN A FIRST STATE AND OPERATIVE TO ASSUME A SECOND STATE WITHIN A PRESELECTED TIME INTERVAL BEFORE AND AFTER OCCURRENCE OF SAID COMMAND SIGNAL, AND A SECOND BISTABLE ELEMENT CONTROLLED BY SAID FIRST BISTABLE ELEMENT AND RESPONSIVE TO SAID POSITION SIGNAL TO ASSUME A FIRST OR SECOND STATE IN ACCORDANCE WITH THE CONDITION OF SAID FIRST BISTABLE ELEMENT. 